THIS INVENTION relates to a dielectric heating device. More particularly, it relates to a dielectric heating device suitable for microwave heating, and to an electromagnetic power source.
According to the invention, there is provided a dielectric heating device, the device including:
a plurality of electrically conductive side walls which are electrically interconnected in use and arranged in series to define a heating cavity, at least one pair of adjacent side walls being inclined to each other at a corner having an included angle selected from the group consisting of acute angles and obtuse angles; and
at least one electromagnetic power source capable of emitting electromagnetic radiation suitable for dielectric heating, the power source being arranged to feed waves of such radiation into the cavity with circular polarization of the waves, to cause the cavity to act as a multimode resonant heating cavity.
The heating cavity may be a heating cavity as described in international patent application number PCT/NL97/00282 published under number WO 97/44988, the contents thereof being incorporated herein by reference.
The electromagnetic power source may be capable of emitting electromagnetic waves in the form of microwaves suitable for cooking foodstuffs; and the device may thus be in the form of a microwave oven. In a preferred embodiment of the invention the electromagnetic power source may include a microwave generator, eg a magnetron of a conventional microwave oven, or the like, and a waveguide having an inlet opening connected to the microwave generator, the waveguide also being connected to an inlet port into the heating cavity, and the waveguide being constructed to convert the linear polarization of the microwaves to a circular polarization thereof, and to guide the microwaves having the circular polarization through the inlet port into the cavity. In other words, the waveguide may thus be arranged to convert electromagnetic waves which have a linear polarization to a resultant electromagnetic wave feed whose waves have a circular polarization and which are fed via the inlet port into the cavity.
The waveguide may be hollow and circular-cylindrical in shape, having an end wall and a curved side wall, the waveguide containing, in its interior, at least one conversion formation for converting microwaves having a linear polarization to microwaves having a circular polarization, the inlet opening of the waveguide being through the curved side wall thereof and the waveguide having an open end for feeding microwaves into the inlet port of the cavity. The conversion formations may be in the form of two panels in the form of blades or plates which extend radially inwardly from opposed inner sides of the circular cylindrical waveguide. Accordingly, the waveguide may include a pair of the conversion formations in the form of diametrically opposed flattened elongated panels, each panel projecting radially inwardly from the inner wall of the cylinder of the waveguide and having a long dimension extending lengthwise along the cylinder, the panels being coplanar and the radially inner edges of the panels being opposed to, and diametrically spaced from, each other. The invention thus extends to an electromagnetic radiation feed arrangement for a dielectric heating device which includes a hollow circular cylindrical waveguide as herein described.
In other embodiments, the waveguide may be in the form of a hollow elongate rectangular waveguide including a microwave inlet which is typically located at a waveguide end wall or at a corner of the waveguide between its ends. An electromagnetic feed from the source inlet may have a linear polarization, the inlet opening of the waveguide being arranged so that the resultant polarization of the waves in the hollow rectangular waveguide is circular. For example, the waveguide may be a hollow box of elongate-rectangular shape, the inlet opening of the waveguide being through a corner of the waveguide between two side walls of the waveguide, at a position between the ends of the waveguide, one end of the waveguide being open for feeding microwaves into the inlet port of the cavity. Instead, the waveguide may be a hollow box of elongate-rectangular shape, the waveguide having an open end for feeding microwaves into the inlet port of the cavity, the opposite end of the waveguide having a wall with a rectangular opening therethrough, the peripheral edges of the rectangular opening being inclined at an angle to the peripheral edges of said wall at the opposite end of the waveguide, a box-like compartment having an open end registering with and communicating with said rectangular opening being mounted on said wall at the opposite end of the waveguide, and the inlet opening of the waveguide being through a wall of the box-like compartment parallel to the long dimension of the waveguide. The invention thus also extends to an electromagnetic radiation feed arrangement for a dielectric heating device which includes a hollow rectangular waveguide as herein described.
It is to be appreciated that the waveguides may be used to feed circularly polarized waves into a heating cavity of any shape or size, e.g. a cavity with a square outline, pentagonal outline, or the like. Preferably, however, the heating cavity is pentagonal in plan view outline when viewed from above in horizontal section.
The invention extends also to an electromagnetic power source capable of emitting electromagnetic radiation suitable for dielectric heating, the power source including an electromagnetic radiation generator which generates electromagnetic waves having linear polarization, and a waveguide having an inlet opening connected to the generator, the waveguide being constructed to convert the linear polarization of the electromagnetic waves to circular polarization thereof and to guide the waves away from the generator.
The electromagnetic radiation generator may be a microwave generator, the power source optionally having a construction as described above with reference to the dielectric heating device of the present invention.